This invention relates to a method for the disintegration and removal of solidified bath material on the residues of prebaked anodes from aluminum electrolysis cells and to an apparatus for carrying out the method.
A prebaked anode consists of a calcinated carbon block provided with holes in the top where an aluminum/steel current-providing rod is fastened either by means of cast iron or a so-called rodding-mix. The anode rod consists of from two to six vertical cylindrical steel nipples connected together by a top steel cross bar which is connected to a vertical aluminum rod.
The carbon block is consumed in the electrolysis cell and the anode has to be removed when the height of the block is reduced to approximately 20%. The top of the carbon block is then covered by a thick layer of solidified bath which sticks to the above mentioned nipples between the carbon block and the steel crossbar. The bath crust can be very hard and consists of a solidified mixture of cryolith and aluminum fluorid with some alumina.
Both the bath material and the carbon residue have to be recovered separately for recycling in the electrolysis process.
The conventional method of breaking down this crust layer is by means of manually operated large pneumatic chisel machines (hammers). This is hard work, where the chisel is partly used as a crowbar.
Furthermore, this method involves considerable environment problems in the form of noise and dust formation even if mechanized as discloed in U.S. Pat. No. 4,119,505 describing an apparatus comprising a pneumatic drill equipped with a precussion tool. Relatively large loads are applied and represent a danger of deformation of the anode rod construction which leads to damaged weld connection between the Al-rod and the steel cross bar. Furthermore, break-up of the anode residue occurs simultaneously, so that it is necessary to separate bath and carbon bits from each other.
Known mechanized equipment, based upon the use of hydraulic pressure power provide, a complicated disintegration operation. The steel nipples themselves are in this case applied as a dolly and must therefore frequently be manually released from the bath in the first place. Besides the above mentioned drawbacks, --deformation of the anode rod assembly and simultaneous breaking of anode residues, poor regularity and low reliability of service are also characteristic for prototypes of mechanized equipment which thus far have been developed and tested.